uprobe-stress: add uprobe stress-testing tool

Implemented a stress-testing tool for uprobes/uretprobes.

It constantly triggers a set of user space functions, in parallel it
attached and detached uprobes and uretprobes to random subset of them.
To make things more interesting we also randomly and in parallel mmap()
/proc/self/exe and fork() process, to trigger all the different code
paths in uprobe-related functionality in the kernel.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

examples/c/.gitignore

@@ -14,3 +14,6 @@
 /lsm
 /cmake-build-debug/
 /cmake-build-release/
+/uprobe-stress
+.gdb_history
+

examples/c/Makefile

@@ -24,7 +24,8 @@ INCLUDES := -I$(OUTPUT) -I../../libbpf/include/uapi -I$(dir $(VMLINUX)) -I$(LIBB
 CFLAGS := -g -Wall
 ALL_LDFLAGS := $(LDFLAGS) $(EXTRA_LDFLAGS)
 
-APPS = minimal minimal_legacy bootstrap uprobe kprobe fentry usdt sockfilter tc ksyscall task_iter lsm
+APPS = minimal minimal_legacy bootstrap uprobe kprobe fentry usdt sockfilter tc ksyscall task_iter lsm \
+       uprobe-stress
 
 CARGO ?= $(shell which cargo)
 ifeq ($(strip $(CARGO)),)

examples/c/uprobe-stress.bpf.c

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "uprobe-stress.h"
+
+char LICENSE[] SEC("license") = "Dual BSD/GPL";
+
+struct counter enter_hits[MAX_CPUS];
+struct counter exit_hits[MAX_CPUS];
+
+SEC("uprobe.multi")
+int uprobe(struct pt_regs *ctx)
+{
+	int cpu = bpf_get_smp_processor_id();
+
+	__sync_add_and_fetch(&enter_hits[cpu & CPU_MASK].value, 1);
+
+	return 0;
+}
+
+SEC("uretprobe.multi")
+int uretprobe(struct pt_regs *ctx)
+{
+	int cpu = bpf_get_smp_processor_id();
+
+	__sync_add_and_fetch(&exit_hits[cpu & CPU_MASK].value, 1);
+
+	return 0;
+}